Feature Request: Add Scroll to Top Button

### Description
Add a scroll-to-top button that appears when users scroll down the page, allowing them to quickly return to the top with a smooth animation.

### Motivation
- Improves user experience on long pages
- Reduces effort needed to navigate back to top
- Standard UX pattern in modern web applications

### Proposed Solution
A floating button that:
- Appears after scrolling 300px down
- Shows circular progress ring indicating scroll position
- Smooth scroll animation on click
- Gradient purple/indigo design matching the app theme
- Hover effects and tooltip

### Design Details
- **Position**: Fixed bottom-right corner
- **Visibility**: Fade in/out based on scroll position
- **Icon**: Arrow up icon
- **Colors**: Purple gradient matching brand colors
- **Accessibility**: Proper ARIA labels and keyboard support

### Technical Considerations
- Use React hooks for scroll detection
- Optimize scroll event listeners (throttle/debounce)
- Ensure accessibility (ARIA labels, focus states)
- Match existing Tailwind CSS design system

Thank you.